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a)17.85-15.17-120
=17.(85-17)-120
=17.68-12
=1156-120
=1036
b)100:[30-(6-1)^ 2]
=100 :[30-5^ 2]
= 100:[30-25]
=100:5=20
c)/-10/+4+3.2^3+(-14)
=10+4+3.8 +(-14)
=14+24+(-14)
=[14 +(-14)]+24
=0+24=24
d)20-[30-(5-1)^ 2: 2]
=20-[30-4^2:2]
=20-[30-8]
=20-22=-2
e)80-(4.5^2-3.2^3)
= 80-(4.25-3.8)
=80-(4.25-3.2.4)
=80-4.(25-3.2)
= 80-4.19
= 80-76=4
g)35-{12-[-14+6-2)]}
=35 -{12-14-6+2}
=35-12+14+6-2
=23+14+6-2
=37+6-2
=43-2=41
a) Không thể vì: \(\dfrac{1}{1^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{100^2}=1+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{100^2}>1\)
b) Ta có: \(\dfrac{a}{b}< 1\) thì \(\dfrac{a}{b}>\dfrac{a-m}{b-m}\)
CM: \(\dfrac{a}{b}=\dfrac{a\cdot\left(b-m\right)}{b\cdot\left(b-m\right)}=\dfrac{ab-am}{b^2-bm}\left(1\right)\\ \dfrac{a-m}{b-m}=\dfrac{\left(a-m\right)\cdot b}{\left(b-m\right)\cdot b}=\dfrac{ab-am}{b^2-bm}\left(2\right)\)
Vì \(\dfrac{a}{b}< 1\Rightarrow a< b\Rightarrow am< bm\Rightarrow ab-am>ab-bm\left(3\right)\)
Từ (1), (2), (3) ta có \(\dfrac{a}{b}>\dfrac{a-m}{b-m}\)
Vậy
\(B=\dfrac{17^{19}-1}{17^{20}-1}>\dfrac{17^{19}-1-16}{17^{20}-1-16}=\dfrac{17^{19}-17}{17^{20}-17}=\dfrac{17\cdot\left(17^{18}-1\right)}{17\cdot\left(17^{19}-1\right)}=\dfrac{17^{18}-1}{17^{19}-1}=A\)
Vậy B > A
a, => 3x-17 = 0 hoặc 3x-17 = 1
=> x=17/3 hoặc x=6
b, => x+1+x+2+....+x+100=205550
=>100x + (1+2+...+100)=205550
=> 100x + 5050 = 205550
=> 100x = 205550 - 5050 = 200500
=>x= 2005
c,=>x+x+1+....+x+2010=2029099
=>2011x+(1+2+....+2010)=2029099
=>2011x+2021055=2029099
=>2011x = 2029099-2021055 = 8044
=>x=4
Có : 3Q = 3+3^2+....+3^101
2Q=3Q-Q= (3+3^2+....+3^101)-(1+3+3^2+...+3^100) = 3^101-1
=>Q = (3^101-1)/2
a)=0 vì 24-42=0 số nào nhân vs 0 cũng =0
b) = 100+(98-97)+(96-95)+....+(2-1)
=100+1+1+....+1(có 46 số 1 )
=100+46
=146
a)(217 + 154).(319 - 217).(24 - 42) = 0
b)100+98+96+...+4+2-97-95-...-3-1
= 100 + (98 - 97) + (96 -95) + .... + (4 - 3) + (2 - 1)
= 100 + 1 + 1 + .... + 1 + 1 (98 : 2 = 49 số 1)
= 100 + 49
= 149
a. 3 . 62 . 8 + 2 .17 . 12 + 4 . 6 . 21
= 186 . 8 + 34 . 12 + 24 . 21
= 1488 + 408 + 504
= 1896 + 504
=2400
a) (18+12.3):9-5
=(18+36):9-5
=54:9-5
=6-5
=1
b) 368+42:7-(23+3)
= 368+42:7-(8+3)
= 368+42:7-11
= 368+6-11
=374-11
=363
c) 324 :322+3.4+3560
=324-22+12+1
=32+12+1
=9+12+1
=21+2
=22
d) 210:25-75:25+3.3
=210-5-3+9
=25-3+9
=32-3+9
=29+9
=38
e) 1449-[(216+184):23].32
=1449-(400:8).9
=1449-50.9
=1449-450
=999
f) 600-400:[118.2-2(50.3-9.16)2]
=600-400:[118.2-2(150-144)2]
=600-400:(118.2-2.62)
=600-400:(118.2-2.36)
=600-400:(236-72)
=600-400:164
=600-100/41
=24500/41 (đề sai)
g) 2001.27+2001.63+2001.10
=2001.(27+63+10)
=2001.100
=200100
h) 64.54+47.64-64
=64.(54+47-1)
=64.100
=6400
i) (-17)+15+68+17+(-15)
=(-17+17)+(-15+15)+68
=0+0+68
=68
j) (-17)+|-5|+|10|+(-11)
= (-17)+5+10+(-11)
=-12+10+(-11)
=-2+(-11)
=-13
k) -75+(-9)+4
=-84+4
=-80
l) -100+(-15+10)+|(-48)+(-22)|
=-100+(-5)+|-70|
=-100+(-5)+70
=-105+70
=-35
a) (18+12.3):9-5
=(18+36):9-5
=54:9-5
=6-5
=1
b) 368+42:7-(23+3)
= 368+42:7-(26)
=368+6-64
=374-64
=310
c) 324 :322+3.4+3560
=32+12+1
=9+12+1
=21+1
=22
d) 210:25-75:25+3.3
=25-3+9
=32-3+9
=29+9
=38
e) 1449-[(216+184):23].32
= 1449-[400:8].9
=1449-50.9
=1449-450
=999
f) 600-400:[118.2-2(50.3-9.16)2]
=600-400:[118.2-2.(150-9.16)2]
=600-400:[118.2-2.(150-144)2]
=600-400:[118.2-2.62]
=600-400:[118.2-2.36]
=600-400:[236-72]
=600-400:164
=Đề sai nha bạn
g) 2001.27+2001.63+20010
=2001.(27+63)+20010
=2001.100+20010
=200100+20010
=220110
h) 64.54+47.64-64
=64.(54+47-1)
=64.(101-1)
=64.100
=6400
i) (-17)+115+68+17+(-15)
=98+68+17+(-15)
=166+17+(-15)
=183+(-15)
=168
j) (-17)+|-5-|+|10|+(-11)
=(-17)+5+10+(-11)
=(-12)+5+10+(-11)
=-7+10+(-11)
=3+(-11)
=-8
k) -75+|(-9)+4|
=-75+|-5|
=-75+5
=-70
l) -100+(-15+10)+|(-48)+(-22)|
= -100+(-15+10)+|-70|
= -100+(-15+10)+70
=-100+(-5)+70
=-105+70
=-35
a) (-17).(24+76)=(-17).(100)=-1700
b) [(-17)+17]+[18+(-38)]=-20
c) [(100-1):1+1].(100+1):2=100.101:2=101.50=5050